Renee Zellweger was fitted with dental retainers to get into character as Judy Garland.

The 50-year-old actress stars as the Hollywood icon - famous for playing Dorothy in 1939 film 'The Wizard of Oz' - in the critically acclaimed biopic 'Judy'.

But to match her ''ravaged'' look, Renee's hair and beauty team took a ''less is more'' approach ''to let the 'Bridget Jones's Diary' star shine in her performance and not detract from it by overloading her with prosthetics''.

The retainers altered the shape of her teeth and modify the way her jaw sat as Judy's teeth were ''quite gnarly.''

'Judy' hair and make-up designer, Jeremy Woodhead said: ''Had we been absolutely accurate, it would have been very distracting.

However, Renee needed to learn how to perform with the teeth in place.

Jeremy added: ''Renee had a set of teeth that she could rehearse with. She spent several weeks with these teeth and by the time we came to film, she was completely used to wearing them, so it didn't impede her.''

The biopic dramatises 47-year-old Judy in the last year of her life as she arrives for a sold-out show at Talk of the Town nightclub.

Renée underwent a diligent transformation to accurately portray the ageing actress in 1968.

Jeremy explained: ''Most of the shading was trying to age Renée's beautiful, flawless face into [Garland's] more ravaged look. There's lots of shading around the jawline to suggest that her face has dropped somewhat, and [we added] eye bags and creasing around the eyes.''

The on-set designer - who has also worked with actors on 'Stan & Ollie' and 'Doctor Strange' - perfected the legend's look with both a day and a stage routine.

He revealed: ''Judy was of an age where she probably wouldn't have gone out of the house without her lashes, eyeliner and lipstick. There are always false lashes, eyeliner and lipstick, but when she is onstage, everything is heightened. The lashes are thicker, longer. The eyeliner is more dramatic, and the lips are a brighter red.''

The blue-eyed Renée also wore brown contact lenses, and her eyebrows were reshaped to look ''theatrical, and [it] also opened up Renée's eyes to match Judy's''.